This invention relates to a torsional damper for a marine propulsion engine and more particularly to an improved torsional damper for use with engines mounted for rotation with their output shafts extending about a vertical axis.
In many applications, an internal combustion engine is operated so that its output shaft rotates about a vertically extending axis. Such applications are common in connection with outboard motors so as to facilitate the driving connection between the engine output shaft and the drive shaft of the outboard motor, which also rotates about a vertically extending axis. With this type of motor, as with many engine applications, it is desirable to incorporate a torsional damper on the engine output shaft for absorbing the pulsations in the output shaft and to reduce vibration and noise. In conjunction with outboard motors, it has recently also been realized that the positioning of the torsional damper at the lower end of the engine output shaft will serve the function of dampening vibrations not only in the engine output shaft but also in the drive shaft and lower unit.
The positioning of the torsional damper at the lower end of the engine output shaft, however, has some difficulties. That is, conventionally, it is the practice to employ a seal between the engine crankshaft and the engine output shaft so as to prevent the leakage of liquids from the crankcase. These liquids may constitute either lubricating oil only or lubricating oil and fuel when the engine is a two-cycle engine.
Since most torsional vibration dampers comprise an inertial member that is bonded to a hub by an elastomeric sleeve so as to provide vibration damping, the accumulation of oil and/or fuel on the damper can give rise to certain problems. That is, the elastomeric material normally employed tends to swell in the presence of fuel and/or lubricants. If the elastomeric material swells, the damper will become, in effect, more rigid and cannot serve its intended purpose.
It is, therefore, a principal object of this invention to provide an improved torsional damper for a marine propulsion engine.
It is a further object of this invention to provide an improved torsional damper for an engine that operates with its output shaft rotating about a vertical axis and wherein the damper will not be prone to deleterious effects caused by lubricant and/or fuel leaking onto it.
It is a further object of this invention to provide an improved and simplified drain arrangement for protecting a torsional damper from the adverse effects of fuel and/or lubricant.